The present invention has as object a process for the preparation of tert-buthylphenols, mainly tert-butyl-4-phenols, starting from phenols and an alkyltert-buthylether.
The tert-butylphenols are useful intermediates in the manufacturing of phenolic resins or antioxidants for rubber and for different plastic materials.
Such compounds are traditionally obtained by alkylation of a phenol by means of isobutilene in the presence of an acid catalyst (according to Kirk Othmer--"Enc. of Chem. Techn." 3rd edition, vol. 4, page 364).
An essential problem encountered in the manufacturing at industrial proportions lays in the need of working with practically pure isobutylene.
As a matter of fact, isobutylene is one of the components of C4 fractions resulting from the vapour cracking of satured hydrocarbons, originated from natural gas or from petroleum, or from the catalytic cracking of the petroleum fraction at refining operations used to produce gasolines. In general, such C4 fractions contain different proportions of isobutylene, butenes and traces of butadiene. Isobutylene can not be easily isolated from such fractions for it is very difficult to separate it, mainly from 1-butene. For such reason, when one wants to obtain a relatively pure isobutylene, one should employ very elaborate separation techniques (selective extraction or absorption) according to Kirk Othmer--"Enc. of Chem. Tech." 3rd edition, vol. 4, pages 346 and next).
Isobutylene may be equally produced by isobutanol dehydration. However, in this event one also obtains an impure product which, when used for alkylating phenols, leads to the formation of phenol by-products, such as derivatives which have a secundary butyl substitute wich are difficult to separate from the compounds searched for which contain a tert-bytil substitute.
It was proposed to introduce methanol in fraction C4, which would come from any one of the cracking operations listed above, to convert isobutylene in situ in methyltert-butylether. In this C4 fraction, eventually previously free of butadiene trances, only isobutilene reacts with methanol. Methyltert-butylether is then easily separated from C4, mainly from butenes (1 and 2). Besides using this ether as an additive for gasolines (unleaded fuel) to increse their octane level, one may also crack it in methanol and isobutylene. Therefore, methyltert-butylether is being increasingly considered as being an intermediate of choice in the preparation of pure isobutylene which one needs for the preparation of tert-butylphenols (according toi Chem and Eng. News, from Jun. 25, 1979, page 35-36).
Analysing the state of the art in the technique, in 1983 we found a patent CS 79-1487, which claims the alkylation of phenols and/or alkylphenols through the reaction of said phenols and/or alkylphenols with a Me 3 COR (where R=H, Me, ChMeEt.) As example, they mention the reaction of phenol with Me3COH in an inert N2 atmosphere (as they use isobutanol, an inert N2 atmosphere is needed to avoid the formation of impurities, besides those impurities which are a result of the reaction itself). The catalyst used could be necessarily chosen among strong inorganic acids, acid cations exchangers and/or phosphor oxides (polyphosphoric acids).
In 1985, we found a paper named "HIGHLY SELECTIVE MONO-TERT-BUTYLATION OF AROMATIC COMPOUNDS" by G. Sartori, F. Bigi, G. Casiraghi, G. Casnati, L. Chiesi and A. Arduini, published by Chem. Ind. (London) (22) 762-3. In this paper are published the reactions of PhR (R.dbd.H, Me, MeO, Cl) with Me3COMe or isobutene in the presence of ZrO4 yielding 85% of 4-Me3CC6H4R. They studied the efficiency of ZrO4 as acid catalyst and, as we will show below, according to the invention of the Petitioner, we obtained tert-butylphenols with catalysts known by those skilled in the art, but with high yield and degree of purity of the high and controlled end product.
Patent DD 87-311221 (Dec. 24, 1987) deals with a process for the preparation of mono, bi-tri-tert-alkylated benzene derivatives using n-alkyltert-alkylethers, and the process temperature, mainly the reaction temperature, in the example 288.degree. C., is much higher that the temperatures used in the Petitioner's process. Those skilled in the art know that equimolar amounts of phenol and acid unfailingly generate corrosion problems due to high temperature, thus demanding a special material for the reactor. There would be also a higher energy consumption, and during the purification process of the final process is made washing with water and later recrystallization which doubtlessly yields a less pure product than thoses processes which use distillation.
In 1980, the Petitioner filed an invention priviledge request PI 8002607 on a process which uses directly alkyltert-butylethers for the preparation of tert-butylphenols. According to this basic invention of the Petitioner, a reaction occurred between alkyltert-butylether with phenol at a temperature ranging between 95.degree. and 180.degree. C. and pressure around athmospheric pressure, in the presence of an acid catalyst such as a Lewis acid, a strong acid with protons or cationic exchange resin of the sulphonic type. The molar ratio alkyltert-butylether/phenol could range from 0,1:1 to 2:1. The phenol alkylation reaction and also transalkylation/isomerization reactions of undesired tert-butylphenols, took place in one single step, i.e. concurrently.
Until 1989, the Petitioner was manufacturing the product paratert-butylphenol, however with control problems in the distillation of end product phase (the samples for quality control were obtained manually by the operators, exposing them constantly to an unhealthy environment), was forced to reevaluate their process, aiming its optimization in order to eliminate industrial hygiene problems, improve the quality of end product, maintaining or even reducing the cost of such process.
The Petitioner developed a new process which solves the problem of industrial hygiene, improves the quality of end product, increasing its degree of purity and, most importantly improved the yield of the process, without any increases in power consumption, therefore not increasing costs.
The Petiotioner was able to increase the yield of the Basic Process (according to PI 8002607) from 78,9% to for instance 94,8%.
In terms of global yield of the process, we may state that it increased from 88.7% (basic process) to 94.8% for reacted phenol and from 80.5% (basic process) to 89.0% for reacted alkyltert-butylether.
Another advantage of such process is the possibility of a total operational flexibility to adjust the quality of paratert-butylphenol thereafter called PTBF, with no yield losses (increasing the value of intermediate product). Therefore, for instance, the Petitioner markets two types of PTFB with different specifications. One technical degree PTFB, which corresponds, for instance to the specifications:
______________________________________ Content of PTFB at least 98.5% Crystallization point 97.5.degree. C. APHA Color, melted 100 maximum Content of dialkylphenols below .8% ______________________________________
And another type called polycarbonate PTBF which obeys the following specifications:
______________________________________ Content of PTBF at least 99.5% Crystallization point 97.5.degree. C. APHA Color, melted 90 maximum Orthotert-butylphenol content below .05% Dialkylphenol content below .055% Phenol content below .1% ______________________________________
As we can see the PTFB polycarbonate content would be a product with a higher degree of purity and nobler uses than technical PTFB.
One of the advantages of this process, is that depending of the purification by distillation of the end product, or better, depending of the cuts of fractions of distillation columns, one may obtain as final product, PTBF technical degree of PTBF polycarbonate degree. According to this process, it is easy to render flexible the type of end product, according to market demands.